Identifying and Managing Cockchafers and Corbies Handouts Information prepared in conjunction with 8x5 field days in June 2005 at “Apsley Park” (near Bothwell) and “Forton” (Epping Forest) By Andrew Hamlet 1, Sarah Campbell 2, Cathy Young 3 & Lionel Hill 4 1 Project Officer, 8x5 Wool Profit Program, Mt Pleasant Laboratories, Kings Meadows, TAS 7249 2 Agricultural Extension Officer, DPIWE, Mt Pleasant Laboratories, Kings Meadows, TAS 7249 3 Entomologist, DPIWE, 13 St Johns Ave, New Town, TAS 7008 4 Entomologist, DPIWE, P.O. Box 303, Devonport, TAS 7310, TIAR Tasmania 1 DEPARTMENT of PRIMARY INDUSTRIES, WATER and ENVIRONMENT Blackheaded pasture cockchafer Acrossidius tasmaniae & Acrossidius pseudotasmaniae Description The adult stage is a shiny dark brown or black beetle 10-12 mm in length. The eggs hatch into C-shaped, white or greyish-white larvae with a characteristic shiny brown or black head capsule and three pairs or legs at the front end. When fully grown in winter they are about 15 mm long. Distribution They are widespread and serious pests of pasture in Tasmania especially in coastal areas and on well-drained, light soils. Damage At night they emerge to feed on the foliage of clovers, grasses and some weeds. It is common for infestations to be confined to well-drained crests in paddocks although continuous infestations over many hectares are prevalent in bad years. Bare patches appear in the pasture from mid-autumn to late winter. Sown perennial species seem to disappear first. Closer examination of the soil surface will reveal tunnel entrances which are usually next to a low mound of thrown-up soil. Unlike corbie burrows there is no silken lining associated with the holes of the pasture cockchafer. Heavy grazing in autumn or winter can aggravate damage because the new regrowth is within easier reach of the larvae. Life cycle The adult beetles emerge from the soil in mid to late summer. Swarming flights are common at dusk on calm, warm evenings. Eggs are laid at this time and hatch after 3-4 weeks. Feeding finishes in early to mid-spring. Monitoring Monitor pastures in May to late June. Look out for bare and overgrazed patches. Pay close attention to sandy or loamy paddocks that had bare patches in January or February, or a history of pasture cockchafer attack. A spade-square sample to a depth of 20 cm is a useful unit to measure with and a series of these should be taken diagonally across a paddock (5 to 20 times) at 20 pace intervals. If average numbers exceed six larvae per spade-square then action should be considered. TIAR Tasmania 2 DEPARTMENT of PRIMARY INDUSTRIES, WATER and ENVIRONMENT Control for blackheaded cockchafer • For best results sprays should be applied before the end of June. Timing is important because larvae do not come to the surface and feed every night. During periods of warm, dry weather (or during a cold, frosty period) they may not feed for several days. Feeding seems to be most intensive on moist nights after rain. Therefore the best time to spray is at the end of a dry spell, a few hours before rain is anticipated. Leave at least four hours for the spray to dry and stick on the pasture. • Chlorypyrifos, Alpha Cypermethrin and Fenitrothion are the three main registered chemicals. Check with your local dealer and follow the label and MSDS. • Maintain pasture cover at 400-600 kg DM/ha. Short, open pasture is more attractive to the egg-laying beetles than rank pasture (whereas the reverse occurs for corbies). A high clover component also favours pasture cockchafer. • Tolerant pasture species include phalaris and cocksfoot. Cocksfoot has good tolerance to surface and root-feeding cockchafers. Phalaris is resistant to all cockchafers and corbies. • Burying surface organic matter through ploughing kills newly hatched larvae. This must be done before May. • In some areas in some years pasture cockchafers are attacked by a pathogenic fungus which often cause population numbers to drop below damaging levels. This fungus, Cordyceps gunnii, is widespread in the State but cannot be relied upon as a control measure at the present time. TIAR Tasmania 3 DEPARTMENT of PRIMARY INDUSTRIES, WATER and ENVIRONMENT Redheaded pasture cockchafer Adoryphorus couloni Description Adults are stout, shiny black beetles about 15 mm long. Larvae are soft, whitish grubs with three pairs of yellowish legs and a hard, reddish brown head capsule. The posterior quarter of the body is a little swollen and greyish in colour. The body wall is transparent. When at rest the body is curved in the shape of a letter C. Newly hatched larvae are only 5 mm long but mature larvae are robust grubs up to 30 mm in length. Distribution Southern Midlands, Derwent Valley, Hobart, South Arm and Flinders Island. It has not been recorded at altitudes above 200 meters. Damage Damage first appears in late March and may be severe by May or early June. Low soil temperatures in winter cause larval activity to diminish before more active feeding resumes in late August and continues until early summer when larvae reach full maturity and finish feeding. Grasses with weak, fibrous roots such as ryegrass are especially vulnerable to damage. In a mixed sward the ryegrass component is often uprooted completely by stock activity. Life cycle Adult beetles emerge from the soil at dusk from later winter to early spring (the end of August until mid-October) and lay their eggs, which hatch in the late spring 6-8 weeks after being laid. Larvae reach the pupal stage in January and dig deeper into the soil to pupate. The pupal stage lasts 6-8 weeks before the beetle emerges from the pupal skin in February- March. However the beetle remains in the pupal cell as a sexually immature adult for about six months until it digs its way to the surface. Monitoring Monitor pastures in late March to June. Look out for dead clumps of grass and increased weedy areas. A spade-square sample to a depth of 20 cm is a useful unit to measure with and a series of these should be taken diagonally across a paddock (5 to 20 times) at 20 pace intervals. If average numbers exceed six larvae per spade-square then consider developing a management strategy, outlined below. TIAR Tasmania 4 DEPARTMENT of PRIMARY INDUSTRIES, WATER and ENVIRONMENT Management for redheaded cockchafer • There are no synthetic insecticides that give effective economical control of redheaded cockchafers since their subterranean feeding habits create difficulties relating to the penetration and stability of chemicals. This contrasts to blackheaded cockchafers which feed above ground and are susceptible to synthetic insecticides. • A biological insecticide (BioGreen™ Granules) is available for red-headed cockchafer. It is a potent strain of a native soil fungus, Metarhizium anisopliae, formulated as a granule that is mixed with seed, but not fertiliser, when sowing pasture. It is best used as a preventative strategy over several years. It is not a quick remedial strategy for one season. • Remove dry pasture residue before autumn (through grazing or cutting hay) to reduce the habitat value for redheaded cockchafer moths. • When damage is noticed in mid-autumn, stock should be removed and the paddock spelled until late winter. This will help prevent all the ryegrass being uprooted by sheep and maintain maximum leaf area needed to re-establish root growth. Although supplementary feed may have to be bought to carry displaced stock over winter, the expense will usually be repaid in superior spring production from the infested paddock. • Diversify feed sources away from total dependence on ryegrass pastures. Eg. Sowing some autumn forage crops, storing extra hay in anticipation of a winter feed shortage aggravated by pests, or sowing down some areas of cockchafer-tolerant pastures. Tolerant pasture species include phalaris, cocksfoot, tall fescue, lucerne and oats. • If conditions are not too boggy, rolling of the infested pasture can be beneficial since this helps the sward re-establish contact with the soil. • Burying surface organic matter through ploughing kills newly hatched larvae. This must be done before May. TIAR Tasmania 5 DEPARTMENT of PRIMARY INDUSTRIES, WATER and ENVIRONMENT Corbie and Winter Corbie Oncopera intricata & Oncopera rufobrunnea Description The brownish-grey moths are about 3 cm long. The front pair of wings bear an intricate pale pattern and the span across the outstretched wings is about 4 cm. Compared to corbie, the winter corbie has a more reddish-brown tinge to the wings. Newly-hatched larvae are about 3 mm long, growing to 6 cm in length by late spring. The body is smooth-skinned and dark greyish or bluish-grey in colour. The smooth shiny head is dark brown. Three pairs of legs are situated behind the head while four pairs of sucker-like prolegs are present on the underside of the middle third of the body. Distribution Corbie ranges widely over all the pastoral areas of the State, particularly the lower Midlands and Derwent Valley. Winter corbie is less commonly a problem in Tasmania than corbie, being most prevalent in the higher rainfall pastures of the north-east and north-west. Damage The two closely related species differ mainly in their life cycles and, therefore, the time of year when they cause damage. Both pests feed on ryegrass, clovers and seed-heads, but generally they avoid flat weeds. Pasture thinning occurs when the larvae reaches about 3 cm in length and is first apparent in May-June for winter corbie and August-September for corbie. Because the larvae chew off pasture at ground level severe damage can result in a short time. The small bare patches that first appear rapidly increase in area of denuded pasture by August (winter corbie), or October-November (corbie).